The Nuclear Regulatory Commission is ending its increased oversight of Energy Northwest's nuclear power plant near Richland, it said in a letter released Wednesday.
The NRC increased inspections after Energy Northwest notified it of a problem with its emergency preparedness program between 2000 and 2011.
Faulty calculations made in the 1990s had compounded for several years, resulting in values that would have overestimated or underestimated the potential radiation offsite in an emergency had the Quick Emergency Dose Projection System been used.
"We're pleased to be back under a normal level of oversight, especially given the strength of our performance in 2012," said Energy Northwest spokesman Mike Paoli.
The plant set records for safety and pushed a record 9.34 million mega-watt-hours of electricity onto the grid last year.
The NRC ended the increased oversight based on the results of a March 22 inspection that concluded the causes of the earlier problem had been identified and that corrections made by Energy Northwest were sufficient to prevent a repeat.
A more rigorous review of calculations for emergency preparedness is done now with an additional level of oversight, according to Energy Northwest.
The inaccurate data would have caused a delay by Columbia Generating Station in recognizing an emergency requiring precautionary actions to protect the public or a more serious emergency with conditions that threatened the public, according to an NRC report.
However, there was no emergency during the years the inaccurate data was used. Energy Northwest also has other methods it would rely on in an emergency to determine the emergency level and the protective actions needed, according to Energy Northwest. That includes direct readings from monitors.
The problem, which occurred under a previous administration of Energy Northwest, was discovered during a self-assessment by the agency in 2011.
The inspection level for the plant is one of the issues expected to be discussed at a public NRC meeting at 5:30 p.m. June 4 at Energy Northwest, 3000 George Washington Way, Richland. The NRC will discuss the Columbia Generating Station's performance for 2012.
-- Annette Cary: 582-1533; email@example.com; Twitter: @HanfordNews